The present invention relates to a fuel control system for use in a so-called torch-ignition type international combustion engine wherein the combustion device thereof comprises a main combustion chamber and an auxiliary combustion chamber provided therein with an ignition plug, said main and auxiliary combustion chambers being in communication with each other through a through-hole. A rich mixture of gasified fuel and air is fed into the auxiliary combustion chamber and a lean mixture of gasified fuel and air is fed into the main combustion chamber, and the mixture of gasified fuel and air in the main combustion chamber is ignited by the combustion flame produced in the auxiliary combustion chamber.
It is known to be preferable as viewed from the point of view of purification of exhaust gases and the fuel consumption rate that in a torch-ignition type internal combustion engine, the mixture of gasified fuel and air fed into the auxiliary combustion chamber must have a good ignitability throughout all of the operating conditions of the internal combustion engine and the mixture of gasified fuel and air fed to the main combustion chamber must be as lean as possible while still producing a desired level of output.
In the prior art, there has been proposed a fuel control system wherein carbureters for main and auxiliary combustion chambers respectively are provided at the same time, or a fuel control system wherein a fuel injection pump is provided for varying the fuel discharge rate dependent on the negative pressure in an air intake manifold which is in communication with the main combustion chamber.
However, the former fuel control system has disadvantages in that the amount of the mixture fed to the auxiliary combustion chamber is far less than that fed to the main combustion chamber, thus amounting to a ratio of 5 to 15 percent thereof to thereby make control of the fuel flow rate difficult, and that the fuel passageway leading to the auxiliary combustion chamber is so small in size as to cause such problems as vapor lock.
With the latter fuel control system, such problems as vapor lock do not occur, but it is difficult to maintain an air-fuel ratio at a desired level since the negative pressure in an air intake pipe is not proportional to the quantity of air flow passing through the air intake duct due to the fact that fuel control is performed dependent upon the negative pressure.
Further, although a fuel injection pump is used, the amount of the mixture fed to the auxiliary combustion chamber is very small as described above, so that the amount of fuel discharged from the injection pump at a time is extremely small. Accordingly, the latter fuel control system has disadvantages in that the production cost of the injection pump is very high, and in that any leakage in the injection pump causes a substantial change in the concentration of the mixture in the auxiliary combustion chamber with the result that the expected object can not be attained.